1. Field of the Invention
The present invention relates to collecting means for powder by-products generated in a decomposition process of a raw material gas in a chemical vapor deposition apparatus.
2. Description of the Prior Art
The chemical vapor deposition (CVD) process has recently been attracting attention as a forming method for the insulating layer for integrated circuits, solar cells and electrophotographic photosensitive members, in view of the usefulness of the process at a relatively low temperature, and of the superiority of the properties of the obtained layer, and has already been partly employed in commercial production in those fields.
The CVD process is generally performed by introducing gaseous raw material molecules into a deposition chamber in which pressure can be reduced by an exhaust system and decomposing the raw material gas with an excitation energy to deposit a desired layer on a desired substrate. In such process, the function of said exhaust system is often hindered by by-products of powder form (hereinafter called fine powder) which are generated in the course of deposition of the raw material gas. As an example, in the formation of a layer of silicon hydride-nitride, silicon hydride-nitride-oxide, silicon hydride-oxide, silicon hydride or silicon-germanium hydride, fine powder containing silicon is generated as a by-product and deposited in the exhaust system, significantly degrading the exhaust ability. It therefore becomes not only difficult to maintain a constant gas pressure in the deposition chamber over a prolonged period but also difficult to obtain a layer having desired properties since the gas pressure in the deposition chamber gradually rises even in a single operation whereby the raw material gas concentration and the discharge between the electrodes become unstable.
The conventional CVD apparatus is generally equipped with a filter in front of the exhaust system in order to eliminate such fine powder generated in the layer deposition, but said fine powder, being soft at a low temperature and easily clogging such filter, not only deteriorates the productivity significantly but also undesirably affects the properties of the deposited layer.